config: replace deprecated AM_CONFIG_HEADER with AC_CONFIG_HEADERS
config: replace deprecated AM_CONFIG_HEADER with AC_CONFIG_HEADERS

Regroup AC statements at the top.

Signed-off-by: Gaetan Nadon <8a8cc541338200f67d4d0bcb65c78b6166649462@videotron.ca>

mad-s/xf86-input-synaptics-absolute,mad-s/xf86-input-synaptics-absolute